JPH01107897A - Biochemical treatment of waste water associated with iron and steel - Google Patents

Abstract

PURPOSE:To efficiently oxidize ferrous ions by maintaining the relation between the concn. of the ferrous ion and the load of the ferrous ions in the waste water supplied to an aeration tank under specific conditions and maintaining the oxidation reduction potential of the aeration tank at >=600mV. CONSTITUTION:The waste water is supplied to the aeration tank in such a manner that the relation between the concn. (g/l) of the ferrous ion in the waste water supplied to the aeration tank and the load (kg/m<3>.day) of the ferrous ions satisfies Fe<2+> load<=-3.05Fe<2+> concn.+112.5 at the time of oxidizing the ferrous ions in the waste water which is associated with iron and steel and has <=5000mg/l ferrous ion concn. by using aerobic activated sludge contg. iron oxidizing bacteria. Furthermore, the temp. in the aeration tank is maintained at 13-33 deg.C and the oxidation reduction potential in the aeration tank is maintained at >=600mV. The efficient oxidation treatment of the high- concn. ferrous ions is then enabled and the treatment is executable in a short period of time with the simple treatment stage and small-scale equipment.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention converts ferrous ions contained in wastewater from surface treatment of steel materials into ferric ions using aerobic activated sludge containing iron oxidizing bacteria. It relates to a method of oxidizing to

(Prior art) In steel works, pickling with sulfuric acid or hydrochloric acid is used to remove scale, dirt, oxide films, etc. from the surface of steel sheets when manufacturing cold-rolled steel sheets or surface-treated steel sheets by galvanizing, tin plating, etc. In addition, pickling treatment is often used to clean steel materials. That is, pickling of steel materials is carried out using a pickling bath of hydrochloric acid, sulfuric acid, etc. with a concentration of about 3 to 20%, and if the pickling bath is used for more than a certain period of time, the pickling ability will decrease, so it must be discarded. After pickling the steel steel material, it is washed with a large amount of water to remove the remaining pickling solution.

Furthermore, in addition to these pickling wastewaters, steelworks also use wastewater similar to the pickling process wastewater (dump liquid from plating baths, rinsing wastewater, ) is emitted. These wastewaters include
In addition to iron ions, zinc, tin, and
Contains plating additives whose main ingredients are metal ions such as chromium and organic compounds. This plating additive is added to the plating bath to obtain good plating properties.
The main component is organic compounds.

Therefore, the pH of wastewater discharged from steelworks' surface treatment processes such as pickling and plating, or other steel-related factories, is extremely low, and in addition to iron ions, zinc (in the case of galvanized plating) and tin are also present. , other metal ions and organic compounds.

Most of the iron ions contained in these surface treatment wastewaters are ferrous (Pet''') ions.

When these wastewaters are discharged into public waters, metal ions such as iron, zinc, and tin, organic compounds indicated by COD, and pH are removed or adjusted to below environmental regulation values before discharge. The conventional method for this is as follows.

First, the alkaline coagulation precipitation method is mainly applied to remove metal ions. That is, these wastewaters are pl+2.
0 to 3.0, and the metal ions mentioned above are almost completely dissolved, so in order to remove these metal ions, a large amount of alkaline agent is added to the wastewater, and the pH of the wastewater is adjusted to 9 to 3.0.
10 to precipitate and remove metal ions as hydroxides.

However, ferrous salts remain dissolved in wastewater unless the pl+ is 9.5 or higher, and even if hydroxides of ferrous salts are produced at pl+ of 9.5 or higher, ferrous hydroxide remains. Since the sedimentation rate of ferrous hydroxide is slow, large-capacity equipment is required to separate the ferrous hydroxide by sedimentation.

Therefore, in order to solve these problems, an alkaline agent such as calcium hydroxide or calcium carbonate is added to the wastewater containing ferrous salts to maintain the pH at 119 to 10, and a large amount of air is blown in for a long period of time to oxidize the hydroxide. Ferrous iron is oxidized to ferric hydroxide. The reason is that ferric hydroxide has p115~
The solubility in the range of 11 is 0.1+ng/j! This is because the solubility is very low compared to ferrous hydroxide, and since this floc has good sedimentation properties, there is little flow out into the treated water.

The treated wastewater is then subjected to solid-liquid separation in a silt settling tank, and the supernatant water is discharged after neutralizing pl+ to a regulation value with sulfuric acid, hydrochloric acid, or the like. The iron, zinc, tin and other metal ions contained in the water treated in this manner are all 0.1 .mu./l or less, which fully satisfies the regulatory values.

(Problems to be Solved by the Invention) However, even in the above treatment method, the oxidation of ferrous hydroxide to ferric hydroxide is often inhibited by the plating and pickling additives. Therefore, it is necessary to separately perform a chemical oxidation treatment using hydrogen peroxide, hypochlorite, etc., or a treatment such as an activated carbon adsorption method.

In this way, conventional wastewater treatment at steel plants includes metal ion precipitation treatment, treatment to oxidize ferrous hydroxide to ferric hydroxide, and chemical oxidation treatment to complete these treatments.
There are many processing steps, and running costs such as the amount of heating air and chemicals are also enormous.

Another problem with the conventional treatment method is that calcium compounds such as calcium hydroxide and calcium carbonate are used in the neutralization coagulation and precipitation treatment, so a large amount of calcium compounds and metal hydroxides such as iron, zinc, and tin are used. The problem is that a very large amount of sludge containing substances is generated, and furthermore, since the sludge contains various metal oxides, there are many restrictions on its effective use.

The present inventors found that the ferrous ion concentration in wastewater was 5000+
A new processing method for solving the above problems at ng/1 or less was proposed in Japanese Patent Laid-Open No. 116385/1985.

This method involves maintaining the relationship between organic compound concentration and activated sludge concentration under specific conditions when treating acidic wastewater with aerobic activated sludge containing iron oxidizing bacteria to oxidize ferrous ions. In addition, the method is characterized in that the amount of aeration during activated sludge treatment is managed using the redox potential as an index.

However, in the above method, the ferrous ion concentration in the wastewater was 50
Since there is a condition of 00 mg/12 or less, when treating dump liquid, the dilution ratio is high and the scale of the water treatment equipment becomes large.

Regarding wastewater treatment using iron oxidizing bacteria, inventions related to mine wastewater, factory wastewater, etc. that do not contain organic matter, such as the Special Publication Publication No. 1973-
There are some disclosures such as Japanese Patent Publication No. 38981, Japanese Patent Publication No. 47-44717, and Japanese Patent Application Laid-Open No. 53-42445, but there are examples in which wastewater containing 5000 mg/β or more of ferrous ions is oxidized to Fe'' by iron oxidizing bacteria. It doesn't fit.

Therefore, the inventors focused on the fact that iron-oxidizing bacteria can be oxidized with 5000+ng/1 or more of ferrous ions under certain control conditions, and invented a high-concentration iron salt oxidation treatment method.

(Means for Solving the Problems) The present invention provides that the ferrous ion concentration is at least 5000 mg.
Using aerobic activated sludge containing iron oxidizing bacteria, the 1
In a method of oxidizing iron ions to ferric ions,
The relationship between the ferrous ion concentration (g#ri) and the ferrous ion load (kg/+vf/day) in the wastewater supplied to the aeration tank satisfies the condition Fe'' load ≦-3,05Fe2+112.5. Supply wastewater so that the temperature inside the aeration tank is 13 to 33℃.
range, and set the redox potential of the aeration tank to 600 mV (silver-
This is a biochemical treatment method for steel-related wastewater that is characterized by a treatment method that exceeds the silver chloride standard (silver chloride standard).

(Function) The present inventors discovered that Fe in wastewater, which can be oxidized by iron-oxidizing bacteria,
2 (■ / liter limit is Fe" loading amount (amount of Fe" to be treated per unit volume of aeration tank), ?ILSS (Mixed
It is thought that there is a close relationship with the concentration of suspended solids in the aeration tank.
As a result of intensive research, the following matters were clarified.

(1) When the raw water Fe"fi degree is 10.000mg/1., the MLSS concentration is 75.000mg/I!, and it is possible to treat the Fe" load up to 80 kg/rTf ・day.
Even if the MLSSI degree is increased further, the Pe'' load amount will not increase.

(2) Raw water Fe215. In OOO+ng/l, ML
SS concentration 100.000 + ng/ 1 and Fe" + load 170 kg/fff' day, ?ILSS: a degree 125.0
At 00 m#, it is possible to process up to a Fe'' load of 1180 kg/ITf·day, but even if the phLssB degree is increased beyond that, the Fe'' load does not increase.

(3) For raw water Fe220,000mg/j2, r+t
, ss6 degree 125,000 rng/I! Fe'' load ff150kg/rri'-day, MLSSfi degree 15
Fe” load ff180kg/ at 0.000 mg/l
It is possible to process up to m days, but beyond that? Even if the ILSSW degree is increased, the amount of Fe'' load does not increase.

In addition, as a result of examining the relationship between raw water Fe2 and Fe'' loading amount while keeping the abdominal SS concentration constant at 100,000 mg/1, we found that the raw water Fe24 concentration was 7.500 to 20,000 mg/1.
In the range of 1, the relationship shown in Figure 1 is obtained, and Fe2
As Fez''' becomes higher, the load amount of Fez''' decreases, and the relationship is expressed by the following equation.

Fe”°load amount (kg/rrf・day)≦3.05F
e2 (g/ 1) +112.5 From these results,
In order to treat wastewater containing high concentrations of ferrous ions using the iron oxidizing bacteria activated sludge method, the MLSS concentration and Fe'' loading must be well balanced.For example, MLSSf
100,000 mg/! If it is kept constant, Fe
It can be treated by setting the "Fe" load so that the above-mentioned formula is satisfied when "1 degree is 20.000 mg/1 or less".

Also, if the water temperature in the aeration tank at this time is less than 13"C, the oxidation reaction will be slow, and if it exceeds 33"C, it will be difficult for iron oxidizing bacteria to inhabit. As shown in FIG. 2, when the voltage exceeds 600 mV (tj! - silver chloride standard), the ferrous ion concentration in the treated water stably decreases, so it must be controlled to be 600 mV or above.

Also, if the pH of the raw water is not 3 or less, it will be difficult for iron oxidizing bacteria to inhabit, so the pH of the raw water should be 3 or less, preferably 2.1 to 2.
Control within the range of 5.

Also, as a nutrient source, nitrogen compounds (N) and phosphorus compounds (P) are each added at 3 mg// per raw water! It is preferable to supply zinc ions and add 1 tng/n or more of zinc ions.

Next, a method for acclimating iron-oxidizing bacteria to wastewater containing 5000 mg/l or more of Fe will be explained.

In JP-A-59-116385, JP-A-60-25589, and JP-A-60-25590, the present inventors discovered that iron inhabiting the sludge of the pickling and Metsuki drainage pits of ironworks. By culturing and multiplying oxidizing bacteria, continuous oxidation treatment of wastewater containing "Fe" was made possible.

The acclimatization method for applying this pickling to the treatment of wastewater that contains iron oxidizing bacteria living in the sludge of the Metsuki drainage pit is to put this sludge into the aeration tank of the activated sludge treatment equipment, For this, Fe21500~2
000mg/l T: Perform batch aeration using wastewater with a pH of 2 to 2.5, and ORP of the aeration tank is 560mV or more.
In addition, when Fe in the supernatant liquid becomes 10 mg/i or less, aeration is stopped, the sludge is allowed to settle, and the supernatant liquid is discharged.
Add 2 to 2.5 liters of waste water, aerate, and repeat the same operation. This batchwise operation is repeated, and when the ORP increases and the oxidation of Fe'' is completed in about 8 hours, the continuous treatment is started.

do.

Continuous treatment starts with Fe" 1500vg/12, and if the Fe" of the treated water becomes 5mg/f or less after 211r treatment, the Fe" concentration of the supplied raw water is increased from 1000 to 1000.
2500■/! Raise it step by step.

By the above method, iron oxidizing bacteria living in the pickling and sludge in the drainage pit of the steelworks are cultured and proliferated.
It becomes possible to continuously treat wastewater containing 5,000 to 20,000 mg/l of e2+.

In addition, 3 tn each of phosphorus and nitrogen are added to the wastewater used for culturing, acclimating, or treating iron-oxidizing bacteria as nutrients for iron-oxidizing bacteria.
g/I! Above, 1 mg/1 or more of zinc ions are added.

The present inventors have discovered that, in addition to phosphorus and nitrogen, zinc is preferable as a nutritional component for iron-oxidizing bacteria. In other words, wastewater that does not contain zinc ions, for example, wastewater generated from the pickling process of hot-rolled steel sheets, contains almost no heavy metal ions other than Fe''. When treatment is carried out, the oxidation rate of Fe"° decreases if the treatment is carried out for a long period of time. However, Z
When n'' is added in an amount of 1 mg/l or more, stable processing is possible without reducing the oxidation rate of re''.

(Example) Wastewater containing ferrous ion concentration 1g/l of 000Il discharged from an electric galvanizing factory was collected in an aeration tank using MLSS1.
oo, 000 K/I! , water temperature 28℃, ORP 600m
The treatment was carried out for 4 hours under the conditions of a Fe24 load of 60 kg/day and a return sludge rate of 100%. In addition, raw water pH is 2.5, P and N are 3 tag/425Zn2+
was added at 5 μ/l. At this time, the ferrous ion concentration in the treated water was 5 .mu./l or less.

Further, by washing the precipitated sludge with water and calcining it at 800''C, iron oxide with FeO purity of 99% or more could be produced.

(Effects of the Invention) As described above, according to the method of the present invention, highly concentrated ferrous ions can be efficiently oxidized from steel-related wastewater,
The treatment process is simpler than conventional methods and can be done in a short time using small-scale equipment. In addition, the amount of chemicals and air (2) are also small, making it possible to reduce running costs. Furthermore, since sludge containing only ferric ions can be generated, the sludge can be used effectively. For example, if the generated sludge is washed with water and fired,
It can be used as a ferrite raw material, valve stem, flocculant, etc.

[Brief explanation of the drawing]

Figure 1 shows the relationship between Fe2 and aeration tank load, Figure 2 shows the oxidation-reduction potential and Fe! ``This is a diagram showing the relationship with concentration. Agent: Patent attorney Masamitsu Akizawa and one other person.

Claims (2)

[Claims] (1) Ferrous ion concentration is at least 5000 mg/l
In a biochemical treatment method for oxidizing ferrous ions to ferric ions using aerobic activated sludge containing iron-oxidizing bacteria in steel-related wastewater containing water-soluble ferrous salts and having a pH≦3. , the relationship between the concentration of ferrous ions (g/l) in the wastewater supplied to the aeration tank and the loading amount of ferrous ions (kg/m^2・day) is Fe^2^ + Loading amount ≦- 3.05Fe^2^+concentration+1
12.5, the temperature in the aeration tank is in the range of 13 to 33°C, and the redox potential of the aeration tank is 600 mV or more (silver-silver chloride standard). Biochemical treatment method for steel-related wastewater. (2) Add 3 liters each of phosphorus compounds and nitrogen compounds to the wastewater.
2. The biochemical treatment method for steel-related wastewater according to claim 1, wherein zinc ions are added in an amount of 1 mg/l or more (as P and N) and 1 mg/l or more.